Electro-cleaning of vanadium



Aug. 2%; 1957 c. M. BROWN ELECTRO-CLEANING OF VANADIUM Sfainiess $feeflH (Cathode) Filed March 16, 1954 Vanadium (Anode) Vanadium INVENTORCHARLES M. BROWN v ATTORNEY G d o n. A

United States Patent ELECTRO-CLEANING or VANADIUM Charles M. Brown,Lewiston, N. Y., assignor toUriion Carbide Corporation, a corporation ofNew York Application March 16, 1954, Serial No.'416,585

' 12 Claims. 01. 204-141 v This invention pertains to vanadium, and morespecifically relates to a method of electro-cleaning this metal inpreparation for its cold working and to apparatus for doing the same.

Because of its high afiinity for oxygen, vanadium acquires a hard andbrittle skin surface when. itis, hot worked. Since oxygen dissolves inthe vanadium to a high weight content during this process, no protectiveoxide coating forms on the metallic surface, but rather thereis formed abrittle layer beneath the oxide surface of the metal. When vanadium iscold worked in this condition, or if an attempt is made to straightendistorted bars of this metal, the oxygen-bearing surface metal cracks.

In the past, vanadium metal bars and rods having a diameter greater than/2 inch have been finished by machining from hot rolled stock. Similarsizes were prepared by cold swaging /2 inch diameter machined parts.Machining the hard surface of vanadium is, however, a difficult as wellas a wasteful practice since special rests and set-ups are necessary inthe machining of long lengths of hot rolled bars, and sincethe ductilevanadium rising along the irregular metallic surface is thereby lost.

It is, therefore, the primary object of this invention to electricallyclean vanadium metal so as to enable it to be cold worked withoutsurface cracking, and simultaneously obtain a maximum recovery ofductile vanadium by eliminating the necessity of surface machining ofthe hot worked metal.

It is another object of this invention to provide an inexpensive andsafe electrolyte which will electro-clean vanadium without pitting itssurface, and which does not require critical current densities.

These objects are attained in the practice of this invention, whichcomprises using vanadium metal as the anode of an electrolytic cellhaving a suitable cathode, an aqueous alkali metal carbonate orbicarbonate electrolyte, applying direct current of a predeterminedvoltage and suitable current density, and allowing electrolytic actionto proceed until the hard, brittle metallic layer on the vanadium metalis removed.

In the drawings:

Fig. 1 represents a convenient embodiment of this invention; and t Fig.2 represents a further refinement of the invention.

Sodium carbonate is the preferred electrolyte for this process, for inaddition to being inexpensive, safe and easy to handle, it effectivelyelectro-cleans vanadium with out pitting. With many other electrolytes,if current density is not properly adjusted, metal is removed, but themetallic surface is adversely affected. With sodium carbonate, currentdensity is not critical in this respect.

An aqueous sodium carbonate solution ranging from 10% to 15% by weightis preferred, but concentrated solutions having as much as 35% sodiumcarbonate, the solubility limit of this compound in hot water, or aslittle as 5%, are also suitable in the practice of this invention.

Other electrolytes having carbonate ions such as potas- "ice siumcarbonate, ammonium carbonate and the like may also be used in thismethod in equivalent concentrations up to their saturation points as mayalso sodium bicarbonate, potassium bicarbonate and other similarelectrolytes capable of providing bicarbonate ions.

Current density values may vary between 0.26 and 1.2 amperes per squareinch. In particular cases, current densities as high as 6 amperes persquare inch may be used. The lower values indicated, however, arepreferred, as they permit the exercise of better control over thecleaning operation, and'avoid possible excessive loss of sound metal.

Quality control of the 'electro-cleaned vanadium metal is accomplishedby hardness tests taken periodically during the electrolytic process.The electrolysis is preferably continued to a point at which thevanadium plate has a maximum of Rockwell B to B85 since this figure issufiiciently low to allow its cold working. These figures are not in anyway critical, however. What is important is that excessively hard andcontaminated outer layers of metal should be removed until a uniformbase metal hardness is reached.

As an example of the practice of this invention, a vanadium platemeasuring inch x 3 /2 inches x 13 inches was formed by hot rolling at1150 C. This plate was prepared for electro-cleaning by sand blastingits surface to remove the heavy oxide film which covered it. The plate10 then served as the anode and a stain less steel strip 112 as thecathode of an electrolytic cell 14 consisting of a hard rubber vat 16filled with a 10% solution of sodium carbonate. A current of 20 ampereswas applied for 22 hours, during which time periodic hardness tests weremade on the vanadium plate. It was found after the complete treatmentthat the smooth and polished surface of the plate was completely free ofits hard surface layer. During this process the plate thickness wasreduced from 0.365 inch to 0.280 inch. It was subsequently cold rolledwithout any difliculty to 0.030 inch.

As a further example of the practice of this invention,

a hot worked vanadium rod, 20, 0.550 inch in diameter by 36 inches inlength was immersed in a steel pipe 22, which in addition to being thecell cathode, also served as the electrolytic cell as shown in Fig. 2..A 20% solution of sodium carbonate was supplied to this pipe, and adirect current of 15 amperes was applied for 4 /2 hours. The originaldiameter of the bar, 0.550 inch, was reduced to 0.440 inch. By the useof this modification of the invention, the brittle surface of the barwas cleaned equally on all sides. The electro-cleaned bar was theneasily conventionally swaged to inch in ditools as is the case where thehard surface is not removed."

It is thus seen that the shape and size of the electro lytic cellsemployed in the practice of this: invention are not at all critical,butmay be varied within wide limits in order to accommodate anodes ofvarious shapes and sizes.

In both examples given above, the recovery of vanadium in cold rolledbars or sheets after the electrolytic step is above as opposed to below50% as occurs when the hot worked vanadium is machined prior to coldrolling.

The present invention makes possible the removal of the contaminatedoutside layer of vanadium of high oxygen content resulting from the hotworking process, by electro-cleaning, using carbonate or bicarbonatesolutions as the electrolyte, thereby eliminating the machining step forrods to be cold swaged to sizes smaller than V2 inch, or for coldrolling vanadium plates to thin sheets.

What is claimed is:

l. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell havinganaqueous electrolyte consisting of ions selected from the groupconsisting of the alkali metal carbonates and alkali metal bicarbonates,applying a direct current of pre-determined voltage and continuingelectrolytic action until the brittle layer of the vanadium metal hasbeen removed.

2. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell, using anaqueous electrolyte consisting of alkali metal carbonate ions at aconcentration range between 5% and 35%, and continuing electrolysisuntil the said vanadium metal has been freed from the hard contaminatedouter layers, and base metal of uniform hardness is obtained.

3. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell having anaqueous electrolyte consisting of alkali metal carbonate ions, applyinga direct current having a density between 0.2 and 6.0 ameres per squareinch and continuing electrolytic action until the brittle layer of thevanadium metal has been removed.

4. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell using anaqueous sodium carbonate electrolyte having a concentration rangebetween 5% and 35%, and continuing electrolysis until the said vanadiummetal has been freed from the hard contaminated outer layers, and basemetal of uniform hardness is obtained.

5. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell, using anaqueous sodium carbonate electrolyte having a concentration of about10%, and continuing electrolysis under a current density ranging between0.2 and 1.2 amperes per square inch until the said vanadium metal hasbeen freed from the hard contaminated outer layers, and base metal ofuniform hardness is obtained.

6. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell having anaqueous potassium carbonate electrolyte, and continuing electrolysisuntil the said vanadium metal has been freed from the hard contaminatedouter layers, and base metal of uniform hardness is obtained.

7. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell having anammonium carbonate electrolyte at a concentration range between 5% andsaturation, and continuing electrolysis until the said vanadium metalhas been freed from the hard contaminated outer layers, and base metalof uniform hardness is obtained.

8. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell using apotassium carbonate electrolyte at a concentration range between 5% andsaturation, and continuing electrolysis under a current density rangingbetween 0.2 and 6.0 amperes per square inch until the said vanadiummetal has been freed from the hard contaminated outer layers, and basemetal of uniform hardness is obtained.

9. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell using anammonium carbonate electrolyte at a concentration range between 5% andsaturation, and continuing electrolysis under a current densityrangingbetween 0.2 and 6.0 amperes per square inch until the saidvanadium metal has been freed from the hard contaminated outer layers,and base metal of uniform hardness is obtained.

it). The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell having anaqueous electrolyte consisting of bicarbonate ions, applying a directcurrent of predetermined voltage, and continuing electo lytic actionuntil the brittle layer of the vanadium metal has been removed.

11. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell having anaqueous sodi um bicarbonate electrolyte at a concentration range between5% and saturation, and continuing electrolysis until the vanadium metalhas been freed from the hard contaminated outer layers, and base metalof uniform thickness is obtained.

12. The method of electrically removing the contaminated, highoxygen-containing surface layer of vanadium metal which comprises makingthe metal to be treated the anode of an electrolytic cell having anaqueous potassium bicarbonate electrolyte at a concentration rangebetween 5% and saturation, and continuing electrolysis until thevanadium metal has been freed from the hard contaminated outer layers,and base metal of uniform thickness is obtained.

References Cited in the file of this patent UNITED STATES PATENTS1,077,696 Fuller Nov. 4, 1913 1,347,897 'Coulson July 27, 1920 1,663,564Rich Mar. 27, 1928 1,731,269 Rich Oct. 15, 1929 2,410,213 Herro et al.Oct. 29, 1946 FOREIGN PATENTS 514,365 Germany Dec. 11, 1930 OTHERREFERENCES Industrial and Engineering Chemistry, vol. 19 (1927), pages786-788, article by Marden et al.

1. THE METHOD OF ELECTRICALLY REMOVING THE CONTAMIUATED, HIGHOXYGEN-CONTAINING SURFACE LAYER OF VANADIUM METAL WHICH COMPRISES MAKINGTHE METAL TO BE TREATED THE ANODE OF AN ELECTROLYTIC CELL HAVING ANAQUEOUS ELECTROLYTE CONSISTING OF IONS SELECTED FROM THE GROUPCONSISTING OF THE ALKALI METAL CARBONATES AND ALKALI METAL BICARBONATES,APPLYING A DIRECT CURRENT OF PRE-DETERMINED VOLTAGE AND CONTINUINGELECTROLYTIC ACTION UNTIL THE BRITTLE LAYER OF THE VANADIUM METAL HASBEEN REMOVED.